Brain Imaging in Multiple Sclerosis _Ultrasonography

Ultrasonography is not currently used in the investigation of MS. Berg et al, however, used transcranial sonography to determine the size of the ventricles in patients with MS and found that an increasing size is correlated with the MRI-determined brain volume, as well as with cognitive dysfunction and clinical disability. Further studies may establish a role for ultrasonography in the prognosis and treatment of patients with MS.^[41]
According to Walter et al, in patients with MS, hyperechogenicity of the substantia nigra and lenticular nucleus correlates with more pronounced MRI T2 hypointensity, which is thought to reflect iron deposition, and a larger bilateral substantia nigra echogenic area is related to a higher rate of disease progression. In addition, a small echogenic area predicts a disease course without further progression over 2 years.^[42]
Walter et al performed the study to determine whether transcranial ultrasonography can identify lesions in deep gray matter in patients with MS and whether such findings can identify the severity and progression of MS. Of 75 patients followed, abnormal hyperechogenicity of the substantia nigra occurred in 41%; of the lenticular nucleus, in 54%; of the caudate nucleus, in 40%; and of the thalamus, in 8%, with similar frequency in patients with relapsing-remitting and primary or secondary progressive MS if corrected for disease duration.

Brain Imaging in Multiple Sclerosis _Magnetic Resonance Imaging

The advent of MRI has revolutionized the diagnosis and monitoring of MS. MRI is well established as the preferred imaging modality for depicting MS lesions. In patients with clinically definite MS (CDMS), MRI demonstrates a high rate of abnormal findings compatible with the diagnosis. In a study by Lukes et al, lesions were demonstrated in 10 patients with CDMS.^[13] In a larger study by Robertson et al, MRI findings were abnormal in 124 of 133 patients with CDMS. Ormerod et al found that 112 of 114 patients with CDMS had abnormal MRI findings and that 102 of 114 had discrete white matter lesions.^[14]
Another major use of MRI has been the evaluation of patients who have had only 1 episode of neurologic impairment and who do not meet the clinical criteria for the diagnosis. The overall risk of developing MS after a single episode of neurologic impairment is estimated to be as low as 12% (2y follow-up study by Beck et al) to as high as 45% (12.9y follow-up study by Sandberg-Wollheim et al^[15] ) or 58% (14.9y follow-up study by Rizzo et al^[16] ).
MRI has been proven to be the most useful investigation for predicting the progression to MS. In a 10-year follow-up study of patients with a clinically isolated event, 45 (83%) of 54 patients with abnormal MRI findings went on to develop clinical MS, whereas only 3 of 27 with normal MRI findings developed MS.^[17]

Degree of confidence

Tintoré et al followed up 70 patients for an average of 28.3 months after an isolated neurologic event and compared various MRI criteria for the diagnosis MS, as defined by Paty et al, Fazekas et al, and Barkhof et al.^{[1, 2, 18, 19]} With the method of Paty et al, which requires 3 or 4 lesions (1 of which is periventricular), the authors reported a sensitivity of 86% but a specificity of only 54%.
The criteria of Fazekas et al resulted in the same sensitivity and specificity. These criteria require 3 lesions with 2 of the 3 following characteristics: infratentorial location, periventricular location, and lesion greater than 6mm. The criteria of Barkhof require 1 infratentorial lesion, 1 juxtacortical lesion, 3 periventricular lesions, and either 1 gadolinium-enhanced lesion or more than 9 lesions on T2-weighted MRI scans. These criteria resulted in a sensitivity of 73% and a specificity of 73%. Thus, as the MRI criteria become more stringent in the diagnosis of MS, specificity increases at the expense of decreasing sensitivity.
In a cohort of the BENEFIT study (a multicenter, randomized, clinical study of 468 patients), the modified Barkhof criteria showed moderate predictive value for conversion to CDMS over 3 years, despite the fact that all patients received interferon beta-1b therapy for at least 1 year. Follow-up MRI was found to be most informative after 9 months in patients without dissemination in space at baseline. The overall conversion rate to CDMS was 42%. Barkhof criteria with the strongest prognostic value were the presence at baseline of at least 9 T2-weighted lesions and at least 3 periventricular lesions.^[20]
According to a study of postmortem MS tissue by Pitt et al, 3-dimensional (3-D), T2*-weighted, gradient-echo (T2*GRE) and white matter–attenuated, turbo-field-echo (TFE) sequences at a 7T field strength can detect most cortical lesions. The 3-D T2*GRE and white matter–attenuated TFE sequences retrospectively detected 93% and 82% of all cortical lesions, respectively.^[21]

Typical findings and pulse sequences

Because of the inflammation and breakdown of the blood-brain barrier in MS lesions, the presence of extravascular fluid leads to hyperintensity on T2-weighted images. Thus, in a patient with MS, MRI scans typically demonstrate more than 1 hyperintense white matter lesion.^{[22, 23, 24, 25, 26]}
Lesions may be observed anywhere in the CNS white matter, including the supratentorium, infratentorium, and spinal cord; however, more typical locations for MS lesions include the periventricular white matter, brainstem, cerebellum, and spinal cord. Ovoid lesions perpendicular to the ventricles are common in MS and occasionally are called Dawson bars or fingers, which occur along the path of the deep medullary veins. Perhaps the most specific lesions in MS are noted in the corpus callosum at the interface with the septum pellucidum.^[27] The imaging characteristics of MS are depicted on the MRI scans below.
Sagittal T1-weighted MRI depicts multiple hypointense lesions in the corpus callosum; this finding is characteristic of multiple sclerosis. Axial T2-weighted MRI in a patient with multiple sclerosis demonstrates numerous white matter plaques in a callosal and pericallosal white matter distribution. Axial T1-weighted, gadolinium-enhanced MRI in a patient with multiple sclerosis demonstrates several intensely enhancing pericallosal white matter lesions compatible with active disease. Axial diffusion-weighted MRI in a patient with multiple sclerosis shows several hyperintense lesions, a feature of inflammatory disease activity. Axial proton density–weighted MRI through the posterior fossa in a patient with multiple sclerosis demonstrates multiple bright foci in the brainstem and cerebellum. Proton density–weighted sequences are highly sensitive for the detection of plaques in multiple sclerosis, especially in the posterior fossa. Axial proton density–weighted MRI demonstrates multiple lesions in a distribution characteristic of multiple sclerosis. Specifically, the periventricular lesions and the more peripheral white matter lesions near the gray matter–white matter junction are typical MRI findings in multiple sclerosis. Axial T1-weighted, gadolinium-enhanced MRI in a patient with multiple sclerosis depicts enhancement of a plaque in the right temporo-occipital lobe, signifying disease activity. Note the C-shaped, or arclike, enhancement, which is fairly characteristic of multiple sclerosis. Sagittal proton density–weighted MRI in a patient with multiple sclerosis demonstrates the characteristic corpus callosal and pericallosal white matter lesions. Axial T1-weighted, gadolinium-enhanced MRI in a patient with multiple sclerosis depicts several enhancing lesions, at least 2 of which show characteristic C-shaped, or arclike, peripheral enhancement. Axial diffusion-weighted MRI in a patient with multiple sclerosis shows several hyperintense lesions, a feature of inflammatory disease activity. Proton density (PD)–weighted MRI has an advantage over standard T2 imaging, because on PD series, MS lesions remain hyperintense, while the CSF signal is suppressed. Therefore, the lesions are easily identified. Depending on the PD technique, the CSF signal is suppressed to a variable degree, rendering it isointense to hypointense relative to the brain parenchyma. This sequence results in substantial suppression of Virchow-Robin spaces, which are perivascular CSF spaces that may penetrate to the subcortical white matter. These spaces may appear as hyperintense spots on standard T2-weighted MRI scans.
Compared with other techniques, nonenhanced T1-weighted MRI is far less sensitive in detecting MS lesions. Acute lesions usually are not depicted at all. With T1-weighted MRI, the clinician can gain a general appreciation of the global cerebral atrophy that occurs with advanced chronic MS. Global atrophy has been suggested to have the strongest imaging correlation with disability.
Chronic MS lesions usually result in localized leukomalacia, and they may appear as hypointense lesions that represent loss of tissue.
Gadolinium-enhanced T1-weighted MRI scans can depict acute, active MS lesions. These appear as enhancing white matter lesions; the presence of an enhancing lesion has been shown to increase the specificity for MS.^{[2, 18]}

FLAIR MRI

Newer MRI pulse sequences and techniques, including fluid-attenuated inversion recovery (FLAIR) MRI and MR spectroscopy, have emerged that are potentially useful in the evaluation of patients with MS.
FLAIR MRI is a heavily T2-weighted technique that dampens the ventricular (ie, free-water) CSF signal. Thus, the highest signals on the sequence are from certain brain parenchymal abnormalities, such as MS lesions, while the CSF appears black. This appearance is different from that on PD-weighted MRIs, on which periventricular MS lesions may appear nearly isointense to the adjacent CSF. (See the image below.)
Coronal fluid-attenuated inversion recovery (FLAIR) MRI in a patient with multiple sclerosis demonstrates periventricular high–signal intensity lesions, which exhibit a typical distribution for multiple sclerosis. FLAIR MRI is a highly sensitive sequence for lesion detection, particularly supratentorially. The greater relative suppression of CSF on FLAIR images compared with PD-weighted series increases the contrast between periventricular lesions and CSF, enhancing their detection. FLAIR has been shown to be superior to PD-weighted sequences in the detection of MS lesions in the cerebral hemispheres. However, PD-weighted imaging remains the investigation of choice for infratentorial lesions.^[28]

MR spectroscopy

Magnetic resonance (MR) spectroscopy uses the characteristic spectra of specific biochemical markers to quantitate organic compounds in vivo. N -acetylaspartate (NAA) is a relatively specific neuronal marker that is present in sufficient concentrations in the brain to be revealed on MR spectroscopic images. By comparing the spectral signal of NAA with that of creatinine (Cr), MR spectroscopic can be useful in assessing neuronal and axonal loss.
Arnold et al noted that the NAA-Cr ratio in the CNS was decreased in moderate to advanced MS. White matter that appeared normal on T1- and T2-weighted images also demonstrated the reduction.^[29] In addition, a normal ratio was noted in the area of a recently active lesion associated with clinical deficits that subsequently resolved. The findings led the authors to propose that MR spectroscopic findings may be able to help identify irreversible axonal damage.
In a study involving 88 patients with MS, De Stefano et al found a strong correlation between disability scores and NAA-Cr ratios.^[30] The ratio exhibited a stronger correlation in patients with MS patients who had milder disability scores. Because MR spectroscopy appears to be capable of depicting changes in white matter that are not detected with routine pulse sequences and because the findings are correlated with disability scores, the use of MR spectroscopy may prove valuable in monitoring patients after treatment and in formulating their prognosis.

Nonstandard MRI sequences

Beyond the standard MRI sequences that are used in clinical practice (T1 +/- Gad, T2, diffusion-weighted imaging, FLAIR), more advanced MRI techniques have been used for research purposes for several years. Many of these series require greater magnetic field strengths over the popular 1.5T, but with the increasing availability of 3T MRI, these sequences will likely find their way more and more into standard clinical practice.
Diffusion tensor imaging (DTI) can utilize diffusion-weighted imaging techniques in different orientations to establish pathology along white matter tracts in the CNS. DTI can identify demyelination and loss of axons along tracts that would otherwise go undetected by conventional techniques.^{[31, 32, 33]} DTI can also identify disease activity in and injury to gray matter structures, which in turn can be used as a markers of disease activity and severity.^{[34, 35, 36, 37]}
Double inversion recover (DIR) sequences can also detect cortical lesions with increased sensitivity over standard MRI sequences, with higher MRI field strengths improving sensitivity.^[38]
Magnetization transfer imaging (MTI) is capable of identifying MS lesions before they can be detected by conventional MRI techniques.^{[39, 40]}

Limitations

In virtually all patients with clinically well-established MS, MRI scans demonstrate the corresponding changes. False-negative findings occur more frequently in patients with early MS and a minimal clinical history of neurologic impairment than in other patients.
O'Riordan et al prospectively found that in 3 of 27 patients with normal MRI findings, MS subsequently developed.^[17] However, the patients with normal MRI findings all developed lesions detectable on MRI scans when the disease became established. Similarly, as patients are followed for longer periods, the rate of false-positive findings decreases, because in many patients with abnormal MRI findings after a single neurologic event, the clinical criteria for MS eventually develop.
Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF), also called nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MR angiography scans. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

Brain Imaging in Multiple Sclerosis _Computed Tomography

Similar to radiography, computed tomography (CT) scanning has had a limited role in the diagnosis of MS and in the treatment of patients since the advent of MRI. CT scans may be used to exclude other causes of neurologic impairment, but they have a low positive predictive value in the diagnosis of MS; thus, the false-negative rate is high.
Prior to the use of MRI, CT scanning, with the injection of double or triple doses of intravenous contrast material, was used in attempts to identify active MS lesions. However, the scans were insensitive for the detection of chronic lesions. CT scans can help in assessing the degree of cerebral atrophy associated with advanced MS, but given the plethora of additional information provided by MRI, CT is no longer used for this purpose.
An acute MS lesion may enhance and appear simply as an enhancing white matter lesion on CT scans, but the appearance is highly nonspecific. When a highly active MS lesion is observed to enhance and possibly exerts mass effect, it can be termed tumefactive (due to the potential for misidentification as a tumor). Because CT scans typically do not help to identify the more chronic lesions, the tumefactive MS lesion may appear as a solitary enhancing mass, which leads to neurosurgical intervention. Fortunately, this situation is relatively uncommon.
In a cohort of 200 patients, Paty et al found that of the 19 who went on to develop clinically definite MS (CDMS), abnormal CT findings were demonstrated in only 9 (47%). In contrast, abnormal MRI findings were demonstrated in 18 (95%). All of the abnormal CT findings were also demonstrated on MRIs.

Brain Imaging in Multiple Sclerosis

Magnetic resonance imaging (MRI) of the brain is useful in the diagnosis and treatment of multiple sclerosis (MS), an inflammatory, demyelinating condition of the central nervous system (CNS) that is generally considered to be autoimmune in nature. White matter tracts are affected, including those of the cerebral hemispheres, infratentorium, and spinal cord. MS lesions, known as plaques, may form in CNS white matter in any location; thus, clinical presentations may be diverse. Continuing lesion formation in MS often leads to physical disability and, sometimes, to cognitive decline.

Preferred examination

Radiologically, the use of MRI is revolutionizing the investigation, diagnosis, and even the treatment of MS (see the images below). Usually, MRI is the only imaging modality needed for imaging patients with MS, and it far surpasses all other tests with respect to its positive predictive value.
Sagittal T1-weighted MRI depicts multiple hypointense lesions in the corpus callosum; this finding is characteristic of multiple sclerosis. Coronal fluid-attenuated inversion recovery (FLAIR) MRI in a patient with multiple sclerosis demonstrates periventricular high–signal intensity lesions, which exhibit a typical distribution for multiple sclerosis. FLAIR MRI is a highly sensitive sequence for lesion detection, particularly supratentorially. Axial T2-weighted MRI in a patient with multiple sclerosis demonstrates numerous white matter plaques in a callosal and pericallosal white matter distribution. Axial diffusion-weighted MRI in a patient with multiple sclerosis shows several hyperintense lesions, a feature of inflammatory disease activity. One of the limitations of using MRI in patients with MS is the discordance occurring between lesion location and the clinical presentation. In addition, depending on the number and location of findings, MRI can vary greatly in terms of sensitivity and specificity in the diagnosis of MS. This is especially true of primary progressive MS, which may not show the classic discrete lesions of relapsing-remitting MS.
A clinician presented with an MRI report that details a few "nonspecific white matter lesions" that are "compatible with MS" is often frustrated with the lack of sensitivity and specificity of such a description. For this reason, imaging findings need to be described in detail, and preferably referenced to one of the published set of diagnostic criteria such as those by Paty^[1] or Barkhof.^[2] Finally, the specific patient's neurologic history and clinical findings must be correlated with the imaging to establish an accurate diagnosis.^[3]
Plain radiographic studies have no positive predictive value in the diagnosis of multiple sclerosis, but occasionally, plain radiographs may be used to exclude mechanical bony lesions. Angiography also has a limited role in the diagnosis and management of MS, but when central nervous system (CNS) vasculitis is considered in a patient with undifferentiated findings, angiography may occasionally be considered.
Cerebrospinal fluid (CSF) analysis for oligoclonal banding or immunoglobulin G (IgG) levels is no longer routine in the investigation of MS, although this test may be of use when MRI is unavailable or MRI findings are nondiagnostic.^[4]

Clinical diagnosis

A diagnosis of MS is made on the basis of clinical findings by using supporting evidence from ancillary tests such as CSF examination for oligoclonal banding and MRI.^{[5, 6, 7]}
Clinically, MS has historically been diagnosed via the demonstration of white matter dysfunction disseminated in time and space.^[8] With the advent of diagnostic laboratory investigations and imaging techniques, the Poser criteria were proposed to establish a degree of certainty of diagnosis in the absence of the 2 clinical attacks by using terms such as possible MS and probable MS.^[9]
With increasing treatment options for MS and better imaging techniques, newer diagnostic criteria have been suggested that allow diagnosis after a single attack coupled with appropriate positive test results. These criteria have been coined the MacDonald criteria.^[10] Essentially, they allow for the second attack in time to be defined by a new lesion appearing on MRI. Also, the MacDonald criteria allow the dissemination in space to be established on the basis of either 9 typical white matter lesions on MRI or 1 enhancing lesion. If CSF studies show increased IgG values or oligoclonal banding, the presence of only 2 typical MRI lesions satisfy the dissemination-in-time criteria.
With respect to the initial clinical presentation in MS, it may vary with the white matter tract involved, and it may include somatic sensory changes, optic neuritis, or weakness, to mention just a few possible neurologic presentations. After only a single attack, the diagnosis of MS is suggested if the first impairment is coupled with positive paraclinical test results, such as those on imaging or CSF studies. Furthermore, the attack must be compatible with the pattern of impairment found in patients with MS, which typically means that the duration of deficit is days to weeks. Worsening of vision due to optic neuritis and subsequent exercise is known as the Uhthoff phenomenon.
Stankiewicz et al correlated brain lesions and clinical status with 1.5T and 3T MRI in 32 patients with MS by use of MRI fluid-attenuated inversion-recovery (FLAIR) sequences, and the authors found that MRI at 3T may provide increased sensitivity and validity in assessment of MS brain lesions. The study showed that FLAIR lesion volume (FLLV) at 3T was higher than at 1.5T. While 3T FLLV correlated moderately and significantly, 1.5T FLLV correlated poorly. When controlling for age and depression, correlations between FLLV and cognitive measures were significant at 1.5T for the Judgment of Line Orientation Test, the Symbol Digit Modalities Test, and the California Verbal Learning Test Delayed Free Recall, but at 3T, correlations were significant and of greater magnitude.^[11]

Clinical course

The clinical course of MS can follow different patterns, and this observation has led to the classification of distinct types of MS. The most common form of MS is termed relapsing-remitting MS, in which progression involves symptoms of neurologic dysfunction frequently followed by partial or complete clinical recovery. In relapsing-remitting MS, global clinical deterioration has traditionally been attributed to cumulative deficit due to incomplete recovery from repeated occurrences of individual relapses. However, this cumulative deficit has been questioned, because evidence increasingly suggests an ongoing background neurologic deterioration that is independent of the relapses.
Occasionally, the course of MS may be more indolent and exhibit a chronic, persistent neurologic deficit without apparent ongoing deterioration or further impairment. Sometimes, this course of MS is called inactive or benign MS, and this form is often observed in patients with prior relapsing-remitting disease.
Another potentially complicating matter clinically is that highly active MS lesions may sometimes demonstrate significant mass effect. Rarely, mass effect can lead to midline shift, herniations, infarctions, and even death. Such a drastic clinical and radiologic presentation can lead to an incorrect preliminary diagnosis and inappropriate neurosurgical intervention. When MS presents in a more fulminant, aggressive manner, it is frequently known as malignant MS or the Marburg variant.
In a prospective study, Lebrun et al followed 70 patients who had their first brain MRI for a variety of medical symptoms not suggestive of MS and found the mean time between the first brain MRI and the first clinically isolated syndrome to be 2.3 years (range, 0.8-5 y). Diagnostic studies of the blood, CSF, and visual evoked potentials were conducted, and clinical conversion occurred in 23 patients: 6 to optic neuritis, 6 to myelitis, 5 to brainstem symptoms, 4 to sensitive symptoms, 1 to cerebellar symptoms, and 1 to cognitive deterioration.^[12] For patient education information, see Multiple Sclerosis.

Medical Radiography Careers

Medical Radiographers are professionals who use complicated imaging apparatus to x-ray various parts of the human body and assist a thorough diagnosis. They execute medical imaging actions to diagnose medical problems. They are also responsible for preparing patients for radiology examinations, positioning them properly under the machines and ensuring accurate doses of radiation. They also have to maintain patient records and radiographic apparatus.
They find employment in medical practitioner offices, clinics, hospitals and diagnostic imaging centers. Their earning ranges from $18.00 to $24.50 per hour. The medical radiography field over the next few years is expected to grow by leaps and bounds. An estimated job opening of 200 vacancies every year is expected. This is because radiography is assuming important proportions in the diagnostic field. It is almost impossible to diagnose a disease without use of radiography.
The American Registry of Radiology Technologists, ARRT, administer certifying exams for Radiology Technologists. In the Arizona State, a certificate from Medical Radiology Technology Board of Examiners (MRTBE) is necessary for employment. Gate Way community college is one of the colleges offering courses in medical radiography. It offers an associate in applied science degree in medical radiography. The degree not only teaches basic imaging principles, but also prepares the student with the job skills necessary for service. After doing a foundation course in medical radiography the student can further advance his career prospects in other imaging professions such as diagnostic medical ultrasound, nuclear medicine technology and magnetic resonance imaging. Apollo College, Colorado Technical University are among many schools and colleges that offer degree or certificate programs resulting in a career as an X Ray technician, Radiographer or a Radiology Technologist.
Thus, medical radiography is a wise career choice today. It ensures recognition in the field of medicine, since no diagnosis is complete without radiographic evidence.

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Diagnostic Radiology - The Advanced Imaging Techniques to Diagnose Fatal Disease

Diagnostic radiology includes the technique and process that are used to generate images of the human body for the clinical purposes. There are certain medical procedures that are used to reveal, diagnose or examine disease. The imaging of the organs and tissues can be performed as a part of radiotherapy by which the images of the organs and tissues are generated to detect the problem in a better way.
Basically, physicians perform two forms of radiographic images, such as projection radiography and fluoroscopy. These two-dimensional techniques cost low in comparison to the 3D tomography. In the wide sense this biological imaging incorporates radiology, nuclear medicine, endoscopy, investigative radiological sciences, thermography, medical photography and microscopy.
Fluoroscopy generates real-time images of internal structures of the body by employing a constant input of X-rays at a lower dose rate. On the other hand projectional radiographs, known as X-ray, are used to determine the type and extent of the damaged bone or fractures as well as they help to detect pathological changes in the lungs.
There is certain imaging techniques used under the diagnostic radiology. The popular techniques are Magnetic resonance imaging (MRI) scan, Computed tomography (CT) scan, X-ray, Ultrasound. Physicians can use radiographic methods for extensive clinical purposes, such as-
Cardiovascular radiology- it is used to diagnose the diseases of the heart and blood vessels. Physicians perform X-ray, CT, MRI and ultrasound for under this treatment procedure.
Breast imaging- this imaging technology can be used for the diagnosis of breast diseases and conditions. Here doctors can perform mammography, breast ultrasound, breast MRI and breast biopsy to heal breast cancers.
Chest radiology- this stream of radiology is devoted to diagnose the diseases related to chest, such as heart and lung cancers. It takes the help of X-ray, ultrasound, MRI, CT and chest procedures.
Gastrointestinal (GI) radiology- this branch of radiology is used for the imaging and diagnosis of the gastrointestinal (or digestive tract) and abdomen. The CT scan, X-ray, MRI, GI procedures are very useful for such biopsy.
Head and neck radiology- this type of radiology is used for the imaging and diagnosis of the head and neck diseases. It includes several radiographic technologies including CT (or CAT), MRI, ultrasound, X-ray.
There are some other forms of diagnostic radiology, such as emergency radiology, genitourinary radiology, musculoskeletal radiology, neuroradiology, pediatric radiology, interventional radiology, radiation oncology, nuclear radiology, etc.

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What Is Digital Radiography?

Radiography is an imaging technique that produces high-quality anatomic images by using x-rays. General radiography is currently a major part of hospital imaging departments and includes abdomen, chest and extremity examinations.

The use of digital radiography has rapidly increased in recent years. Computed radiography provided a cost-effective transition mode from the traditional film (from the year 1895) to the direct digital radiography (DDR), by using conventional x-ray equipment. Direct digital radiography is a cassette-less imaging system and is ideal for applications where high throughput is of primary importance. The direct digital radiography system should allow usage of all general radiography diagnostic applications.

The major components of a digital radiography system are as follows:
1. X-ray generator
2. X-ray assembly
3. Table trolley or other device to support the patient
4. Support for the x-ray tube assembly
5. Detector which converts the x-rays to an image
6. Acquisition workstation to process and display the image

There is a variety of technologies on which the direct digital radiography is based:
1) Indirect conversion detector: x-rays are converted to light scintillations and light is converted to electric signals.
2) Direct Conversion Detector: x-rays are directly converted to electric signals.
3) Linear Scanning Detectors: A fan beam of x-ray scans the examined area synchronously with a slot of detectors.

Due to the structure of the detectors, indirect and direct x-ray conversion detectors are frequently referred to as flat panel detectors (FPD's). There are also portable digital cassettes available, either sold as part of a system or can be retrofitted to an existing CR or film/screen room. Portable detectors can be used in conjunction with an x-ray mobile unit. Such detectors can be connected to a review work station by wire or via a radio link.

Most of the digital detectors will need some level of environmental control. This may be in terms of operating temperature range, rate of exchange of temperature and/ or relative humidity.

As the original image from the detector is likely to be unsuitable for operating; image processing needs to be applied. A flat field correction is usually applied to the raw image to account for variations in the detector sensitivity across its full area. Also, a number of individual pixels may be defective.

The majority of direct digital radiography units are provided with automatic exposure control (AEC) to provide the selected dose to the detector. This may use a conventional AEC detector or the actual image detector to determine the correct dose level. It is essential that the AEC operates in a reliable and consistent manner and that it is correctly set up for the detector of the exposure.

Optimization is the process of identifying the necessary radiation dose level to provide adequate clinical information for a particular examination. Optimization depends on a range of both clinical and technical factors.

In modern digital radiography systems there is an inbuilt detector dose indicator. The detector dose indicator (DDI) gives an indication of the level of radiation exposure received by the detector. This is useful for monitoring that the exposure is in the correct range for optimal image quality and for undertaking QA.

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This blog is about clinical radiography. Clinical radiography is now in its advanced stage. It starts from simple X ray to the most advanced MRI. I just like to share my experience with clinical radiography. I am in clinical radiography for the last 15 years. Many things I have to share with you. My posts will disclose all of them.... Read on.